notation reference - text scripts ?

[corallina]

In the notation reference manual   1.8.1 Writing Text
the page  Text scripts    has examples for

text above the staff   note^\markup

text below the staff   note_\markup
text below the staff   note-\markup               first example
a4-\markup scherz

Is the usage of both the dash and the underscore intended for some reason?

Thanks and just curious as the first time I saw the dash I thought it might
be an error so I looked around for the reference